LHCb - Large Hadron Collider beauty experiment

Welcome to the LHCb experiment

LHCb is an experiment set up to explore what happened after the Big Bang that allowed matter to survive and build the Universe we inhabit today

Fourteen billion years ago, the Universe began with a bang. Crammed within an infinitely small space, energy coalesced to form equal quantities of matter and antimatter. But as the Universe cooled and expanded, its composition changed. Just one second after the Big Bang, antimatter had all but disappeared, leaving matter to form everything that we see around us — from the stars and galaxies, to the Earth and all life that it supports.

Take the LHCb Virtual Tour

22 July 2011 (1): Hunting for New Physics continues

LHCb physicists continue their search for new physics, see 8 April 2011 news for introduction. They have
presented updated results during the International Europhysics Conference on High Energy Physics (EPS-HEP) at Grenoble this week.
The LHCb physicists have succeeded in setting the limit for an enhanced decay rate of the strange beauty particle B0s,
composed of a beauty antiquark (b) bound with a strange quark
s, into a μ+ and μ- pair, as low as about 4 times the rate calculated within
the Standard Model (limits 1.2x10-8 at 90%CL and 1.5x10-8 at 95%CL for experts). This result was obtained
from the analysis of about 8 times more data than in the previous analysis.

click the image for higher resolution

The computer reconstructed images above show the most significant event compatible with the strange beauty B0s decay into muon pair seen as a pair of purple tracks
traversing the whole detector. The right hand image shows a close-up around the proton-proton interaction point from which many tracks originate.
The B0s decays about 1 cm from the proton-proton collision point into two muons (purple tracks). The invariant mass of muon pair corresponds to the
B0s mass.
The number of observed B0s candidates is slightly above the background predictions and compatible with the expected signal predicted by the Standard Model (SM) theory.
This analysis is much more sensitive than previous experiments, and although large deviations (by more than a factor 4) from the SM are excluded, there is still plenty of room for new physics contributions.
LHCb physicists are expecting to be able to analyse about three times as many events by the end of 2011, and about ten times more by the end of 2012, to give a final answer for the
possibility of a new physics contribution to this interesting rare decay.

22 July 2011 (2): Hunting more for New Physics

LHCb Physicists have also presented results of their search for new physics using the B0d
(composed of a beauty antiquark (b) bound with a down quark d)
decay into an excited K meson, K*, and a μ+ and μ-.
The partial rate as a function of the square of the di-muon invariant mass (q2) and the di-muon forward-backward asymmetry (AFB) can both be affected in many new physics scenarios.
The variable AFB indicates whether more or fewer muons of one sign are observed in the forward direction than in
the backward direction. The distribution of AFB in function of q2 is shown below.

click the image for higher resolution

The LHCb precision measurements shown in black are in agreement with the Standard Model (SM) theory and
indicate for the first time that the asymmetry is changing sign as predicted by the SM.
The results of measurements by other experiments are presented in the figure on the right hand side.

22 July 2011 (3): Different properties of matter and antimatter

An important part of the LHCb physics programme is reserved for studying differences between the properties
of matter and antimatter (CP violation for experts). At the EPS-HEP
meeting in Grenoble this week the LHCb physicists have presented distributions in which these differences can be clearly seen.

click the image for higher resolution

The blue line follows the measured points. After background subtraction (slightly sloping black line from left to right)
the Kπinvariant mass distribution is divided into different components
shown in different colours. The different charge combination of K and π indicates if the decaying B particle is a matter or an antimatter particle. The red curve in the upper plots shows the decay rate of B0d (matter, left plot)
and anti-B0d (antimatter, right plot). The horizontal red dotted line helps to show that the decay rates of
matter and antimatter B particles to Kπ mesons are different. The green distributions in lower plots show that the difference between matter and antimatter decay
rate is also observed in B0s decays to Kπ.

1 June 2011: Pierluigi Campana - new spokesperson for the LHCb collaboration

Pierluigi Campana from the Istituto Nazionale di Fisica Nucleare in Frascati,
begins his 3-year tenure as LHCb spokesperson this June.
He replaces Andrei Golutvin, from Imperial College London and
Russia’s Institute for Theoretical and Experimental Physics.
As the new voice for the collaboration, Campana will lead the experiment through
what should prove to be a very exciting phase.

Read more details in the CERN Bulletin article in English
and in French.

8 April 2011: Hunting for New Physics

Quantum mechanics allows energy non-conservation during a very short time, typical in particle collisions.
This opens up the possibility to study signal for the existence of particles for which there is insufficient energy to produce them directly.
This feature is used by LHCb physicists to search for heavy particles expected in new physics models - models that
describe physics outside the Standard Model (SM) of particle physics. Since the effects of new physics are expected to be
very small, LHCb physicists are looking for modifications of the properties of very rare SM processes which can be calculated
with high precision. The rare decay of the strange beauty particle B0s, composed of a beauty antiquark (b) bound with a strange quark
s, into a μ+ and μ- pair is an excellent candidate.
Only one out of 3*109 B0s mesons should decay into a μ+μ- pair according to precise SM calcutions. This rate could be higher if
new physics particles, such as those in models with an extended Higgs sector, for example, were to influence this decay.

LHCb physicists have not seen these decays in the data taken during the 2010 run
and were able to set a limit which is about 19 times higher than the SM prediction, that is, the limit close to the one set by the Fermilab experiments CDF and D0
after many years of data taking. The figure below was used to set this limit at different levels of statistical probability.

click in the image to get it in higher resolution

LHCb physicists expect to observe the B0s mesons decay into μ+μ- pairs with the rate
calculated within the SM using data taken this year and in 2012. An earlier observation of a higher rate will give interestng evidence for new physics.

25 March 2011: LHCb movie

LHCb live and LHCb physics are presented in a short movie (about 15 min) "LHCb - the beauty experiment", available at YouTube and
CDS. The YouTube version allows you to choose subtitle language (cc just below the movie window), as well as the image resolution including High Definition version 1080p.

15 March 2011: Oscillating Strange Beauty or how matter turns into antimatter and back

Using data collected in proton–proton collisions at the LHC at a centre-of-mass energy of 7 TeV LHCb has observed a fascinating feature of quantum mechanics.
The strange beauty particle (matter) B0s composed of a beauty antiquark (b) bound with a strange quark
s turns into its antimatter partner composed of a b quark and an s antiquark (s) about 3 million million times per second (3*1012).
The B0s particles have been identified through their decay into strange charm Ds particles (composed of a charm quark c bound with a strange s
antiquark) and one or three πs.
Of course, LHCb observes B0s particles and antiparticles only during their short lifetime in which
they travel about 1 cm in the LHCb detector.

The plot shows the observation of these oscillations when all data have been folded into one oscillation period.
The variable Amix is proportional to the difference between the number of events in which the produced matter(antimatter) B0s particle had the same identity during its decay, and
the number of events in which it had not, as a function of its lifetime.

click in the image to get it in higher resolution

The B0s oscillations were observed for the first time by the Fermilab experiments CDF and D0 in 2006, see Press Release article.
The oscillation parameters measured by the LHCb Collaboration show agreement with those measured at Fermilab.

Using data collected in proton–proton collisions at the LHC at a centre-of-mass energy of 7 TeV, the LHCb experiment has observed two new rare decay modes of B0s mesons for the first time.
The decay B0s → J/ψ f0(980) will be important for studying differences between properties of matter and anti-matter (CP violation for experts)
in the B0s system, while the decay B0s → D*–s2Xμ+ν will be valuable for testing predictions of strong interaction (QCD) theory.

The first new decay mode observed is of the decay B0s → J/ψ f0(980).
The B0s consists of a b antiquark (b) bound with an s quark, and can decay to a J/ψ (cc) together with an ss state,
which can be a φ or, more rarely, an f0. While the φ decays to K+K–, the f0 decays to π+π–. The figure shows the enhancement in the π+π–invariant mass distribution
in the region of 980 MeV indicating an observation of f0(980).

click in the image to get it in higher resolution

The observation of these two new decay modes demonstrates that the LHCb experiment is already competitive in the field of heavy flavour physics. Great progress is expected with the larger data sample due from the coming run, with the potential to constrain, or even observe, new physics.

Read more details in the CERN Courier article, which also includes description of the second decay.

27 October 2010: Exotic mesons

In 1964 Murray Gell-Mann and George Zweig proposed the quark model (QM) in which mesons,
like π mesons, are formed from quark and anti-quark
pairs and baryons (like protons) from three quarks. The model is very
succesful, but recently particles which could not be classified in this model have been discovered. LHCb has observed
one of these exotic state candidates called X(3872) using its decay into a J/ψ meson (see 6 September news) and a π+π- pair. The J/ψ decays
in turn into a μ+ and
μ- pair. The invariant mass of J/ψπ+π- is shown in the figure below. The left enhancement at
the mass of 3686 GeV is consistent with the QM bound state ψ' of charm and anti-charm quarks,
the right one at the mass of 3872 GeV has properties that are very difficult to reconcile with the Gell-Mann Zweig QM. Possible explanations include a meson-meson molecule (DD* for experts) or multi quark anti-quark system
(diquark-diantiquark tetraquark meson for experts).

this plot was made using all data taken in 2010, click in the image to get it in higher resolution, click here to see original plot.

The particle with the mass of 3872 Gev was first observed by the BELLE collaboration in 2003 and is called X(3872). The observation of this
particle at this early stage of data taking by LHCb confirms the excellent performance of the LHCb detector and data analysis.

6 September 2010: Beautiful atoms

The LHCb has observed beautiful atoms. The atoms are bound states of the beauty quark and anti-beauty quark. The atoms are
bound by the strong force, the force which also binds quarks inside proton. The beautiful atom is 10 times heavier than the proton
(yes, we can create mass from energy using famous Einstein formulae E=mc2), has a size sligtly smaller than
the size of the proton but about 100 000 times smaller than the size of the hydrogen atom which is composed of a proton and an electron and is bound by
the electromagnetic force. Just like ordinary atoms beauty and anti-beauty quarks form different quantum states with different
angular momenta and different spin orientations (see figure below right). Only the states marked 1S, 2S and 3S are observed
at LHCb by detecting their decay into a μ+ and
μ- pair (left).

The figures above show the invariant mass of μ+ and μ- particles (left) and the schematic view of the beautifull atom quantum states (right),
click in images to get them in higher resolution. The invariant mass plot was made using all data taken in 2010, click here to see original plot.

The beauty-anti-beauty atom, called "Upsilon" was discovered in 1977 at the proton-antiproton collider at Fermilab near Chicago.

The states 1S, 2S and 3S do not decay into Beauty Particles since their mass is lower than the sum of masses of Beauty and anti-Beauty particles
(BB threshold in the figure). On the other hand the state 4S does decay. This feature is used by the experiments BABAR and BELLE
producing the 4S state at e+e-colliders as a source of Beauty and anti-Beauty particles.

The charm and anti_charm quarks form two bound atom states 1S and 2S called J/ψ and ψ' observed at LHCb through their decay into a μ+ and
μ- pair (left) and a e+ and
e- pair (right).

22 July 2010: From a B to Z, LHCb explores the particle alphabet

LHCb has unveiled pictures of a Z boson inside the experiment. This boson is one of the best understood of all particle species. It shows us how the forces of electricity, magnetism and radiation are connected inside the Standard Model, our theory of particle physics. Measurements of how often we see Z bosons inside LHCb will provide a sensitive test of how well our theory describes this particle at the record breaking energies of the LHC.

click in images to get them in higher resolution

In this picture the Z boson has decayed immediately to two muons μ, shown by the thick white lines which point to the green muon chamber hits in the outer circle of the Eolas display (described in 10 June 2010 News). Not much else happens inside LHCb when a Z is at work – only a few other particles are visible – and this makes it an easy particle to find. We’re looking forward to collecting more of them now, and really testing how well the Standard Model performs for us.

12 July 2010: LHCb is younger!

The average age of the LHCb Collaboration members has strongly decreased after arrival of the LHCb summer students seen
below in front of the Globe of Science and Innovation.
The Summer Students follow the lectures given at the first floor of the Globe in the morning. During the breaks they can
visit the new CERN exhibition "Universe of Particles"
located on the ground floor and the rest of the time they make an important contribution to the LHCb data taking and data analysis.

10 June 2010: The W boson in action

LHCb has taken its first snapshots of the W boson in action. This particle conveys the weak force, which makes certain forms of radioactivity possible. It is shown here having decayed to a muon μ
(shown as a straight white line, pointing to the filled green muon detector hit circles in the 2D picture, and as a red line pointing to blue muon hits in the 3D picture), which we see, and a neutrino ν, which we don't, with very little else around it.

click in images to get them in higher resolution

Eolas (gaelic for 'knowledge') is a 2D view of a collision inside LHCb. It is a transmogrified view, chosen to illustrate where particles deposit energy as they fly
outwards from the collision point. The radius represents flight through the detector along the beam direction - through the tracking detectors, then the first muon chamber, then the electromagnetic
and hadronic calorimeters, and finally the last four muon chambers. The φ angle represents the angle in the x,y direction perpendicular to the beam.
Information is colour coded. Particle tracks are shown by the dashed lines. The transverse momentum of the particle is shown by the solid white long along this path -
the higher this is, the longer the solid white bar is. Yellow bars show energy deposited in the electromagnetic calorimeter, cyan energy deposited in the hadronic calorimeter.
Deposits in muon chambers are illustrated by green circles. If these are filled, they are associated with a particle track passing through them.

We will use samples of W bosons to test our theory of particle physics, the Standard Model, to high precision. This is exciting because we don't know yet if our theory holds at LHC energies - if it doesn't, if there are new particles to find in nature, we'll see W bosons behaving in a way we don't expect. With these first snapshots taken, we're on our way to finding out.

7 May 2010: Strange Beauty and Charm

LHCb has reconstructed an event having all characteristics of a Strange Beauty Particle decay! A computer view of this event is shown below. The Strange Beauty Particle (called Bs) is composed of an anti-quark b (b is for beauty)
and a quark s (s is for strange). It is produced by the collision of two 3.5 TeV protons from the LHC at a location marked as "PV" (Primary Vertex), together with many other particles (not shown). The Bs
decays after travelling about 1.5 mm into three particles called μ-, Ds+ and neutrino ν at a place marked "SV" (Secondary Vertex).
The ν is not detected since it can even traverse the whole Earth without any interaction.
The Charm Particle Ds+ is composed of a c quark (c is for charm) and anti-quark s. The Ds+ particle decays in turn after travelling 6.5 mm into three
long lived particles K+, K- and π+
in a place called "TV" (Tertiary Vertex). The K+, K- and π+
are traversing the LHCb detector where the tracking system is used to reconstruct their trajectories with such a very high precision that it is clear that the particles come from three different places called vertices.

21 April 2010: First reconstructed Beauty Particle

LHCb has reconstructed its first Beauty Particle! You can see below a computer view of this event in two projections (images on the left hand side). The Beauty Particle (called B+) is composed of an anti-quark b (that has a very short
lifetime of 1.5 thousandth of a nanosecond!) and a quark u. It is produced by the collision of two very high energy protons from the LHC at a location marked as "Primary vertex", together with many other particles (shown in black). The B+
decays after travelling about 2mm into two particles (called J/ψ and K+) at a place marked "B decay vertex". The J/ψ particle
decays in turn immediately into two long lived particles called μ+ and μ-. The μ+ , μ- and K+
are traversing the LHCb detector where the tracking system is used to reconstruct their trajectories with such a very high precision, that it is clear they do not come from the primary vertex. The fact that the reconstructed tracks do not cross exactly
in two points reflects experimental precision of computer reconstruction. The real particle tracks originate at the two vertices. The images on the right hand side show the same event when the tracks from the "Primary vertex" are forced to come from
the "Primary vertex".

click in images to get them in higher resolution

The LHCb physicists have collected about 10 million proton-proton collisions in order to find this first Beauty Particle. The reconstruction of each event is not easy, there are about 100 particle tracks reconstructed in this event, see full event display below.

More details: LHCb physicists have calculated invariant mass of μ+ and μ- particles from the "B decay vertex" and found that it correspond to the J/ψ mass, see below invariant mass distribution
of all μ+ and μ- pairs with the peak corresponding to the J/ψ decays. The reconstructed invariant mass of J/ψ and K+ is 5.32 GeV, in agreement with to the known B+ mass, 5.5 times higher than the colliding proton mass
but 650 times smaller than the colliding proton energy (yes, we can create mass from energy using famous Einstein formulae
E=mc2).

First

30.3.2010

Both proton beams made a full turn of LHC on Feb. 28th. A new period of great measurements with LHCb has started again and will continue for 18-24 months. On March 18th both beams have been accelerated to 3.5 TeV,

3.5x3.5 TeV

30.3.2010

see TV footage with preparation for collisions and photo above taken just after the first collisions at 12:59 on March 30 (click on picture to get it in higher resolution).

International

On March 8th, during during International Women's Day, many many women have been present in the LHCb control roon, ...

Women's

8.3.2010

see the photos taken at the LHCb control room (click in pictures to it in higher resolution, click here to get other photos), the video interview with Monica Pepe-Altarelli here, ...

Day

8.3.2010

the LHCb women poster (click in image to get higher resolution), and the CERN and the Fermilab Web pages.

2009 News

Below you may find interesting computer reconstructed events observed with the LHCb detector during the LHC restart period in November and December 2009. Click on picture to see it in higher resolution version.

Protons have ended to circulate at LHC on December 16th.

1.2 TeV collisions at LHCb

14.12.09

On December 14th 1.2 TeV proton beams have collided at LHCb during LHC machine studies. Many LHCb subdetectors, except for sensitive silicon detectors, recorded the world's highest energy pp collisions. Other events can be found here.

proton interactions with gas

12.12.09

Position of proton interactions inside the vertex detector with residual gas are shown in blue or red, proton-proton interactions in green (more details).

K0 reconstruction

12.12.09

So called "strange particles" are produced in the proton-proton collisions and decay inside LHCb detector into two other particles reconstructed as red tracks (more details).

High multiplicity events

12.12.09

A high multiplicity event with three muon tracks (green) recorded on December 12th. Other events can be found here.

More proton-proton collisions

8.12.09

On December 8th many long tracks were reconstructed using the detectors along the whole length of the LHCb. Collision vertex is clearly observed (bottom left). The tracks are curved in the magnetic field allowing measurement of the track momentum (top left). Other events can be found here.

More proton-proton collisions

6.12.09

On December 6th protons have again collided at LHCb. Few modules of sensitive LHCb Vertex Locator VELO recorded tracks clearly indicating proton-proton collision vertex location (see picture left bottom). Other reconstructed events can be found here.

RICH rings

6.12.09

LHCb RICH detectors are used to identify particles. The circles show possible position of measured points for different kinds of particles traversing the detector. The measured points clearly choose one possibility for every circle and in this way allow to identify particles.

First proton-proton collisions

23.11.09

A proton-proton collision candidate event. On November 23 protons from two beams circulated at LHC and have collided at LHCb.

First proton interactions

A splash from the LHC beam

21.11.09

LHC has restarted on November 21st. Two LHC beams have made a full turn of the LHC. Afterwards, after synchronization with the LHC accelerating system (RF capture in technical language), the beams made few hundred turns. During LHC operation LHCb has recoded splash events. The movie (click on picture) shows what LHCb detector has recorded every 25ns (1/(40 000 000) s) for a particular splash event; see individual events here.